Photoflash lamp

ABSTRACT

A percussive-type photoflash lamp in pH the inner wall of the lamp envelope is provided with an indicator spot sensitive to the combustion products of the fulminating material of the primer. The spot comprises a pH indicator sensitive to these combustion products and a fluorescent pigment insensitive thereto. Exposure to the combustion products of the fulminating material causes a change in the pH indicator and thus either masks or exposes the fluorescent pigment depending upon the particular indicator used. In either case, the responsiveness of the fluorescent pigment to ultraviolet light or the lack of it constitutes an automatic means for ascertaining the condition of the fulminating material.

United States Patent 3,195,326 7/1965 Shaffer 43l/l3 Primary Examiner-Edward J. Michael Attorneys-Norman J O'Malley and Joseph C. Ryan ABSTRACT: A percussive-type photoflash lamp in pH the inner wall of the lamp envelope is provided with an indicator spot sensitive to the combustion products of the fulminating material of the primer. The spot comprises a pH indicator sen sitive to these combustion products and a fluorescent pigment insensitive thereto. Exposure to the combustion products of the fulminating material causes a change in the pH indicator and thus either masks or exposes the fluorescent pigment depending upon the particular indicator used. [neither case, the responsiveness of the fluorescent pigment to ultraviolet light or the lack of it constitutes an automatic means for ascertaining the condition of the fulminating material.

PHOTOFLASH LAMP lamps and more particularly to those of the percussive type.

Generally speaking, a percussive-type photoflashlamp comprises an hermetically sealed, light-transmitting envelope containing a source of actinic light and having a primer secured thereto. More particularly, the percussive-type photoflash lamp may comprise a length of glass tubing constricted to a tip at one end thereof and having a primer sealed therein at the other end thereof. The length of glass tubing which defines the lamp envelope contains a combustible such as shredded zirconium foil and a combustion-supporting gas such as oxygen. The primer may comprise a metal tube and a charge of fulminating material on a wire supported in said tube.

The fulminating material generally comprises a mixture of red phosphorus, potassium chlorate and a powdered metal such as zirconium. It must be extremely sensitive to impact ignition to insure high lamp reliability of flashing with the desirably low impact energies delivered by the firing mechanism. At the same time, the metal tube of the primer is thin walled and soft so as to minimize the required impact and afford the maximum lamp reliability. Operation of the percussive-type photoflash lamp is initiated by an impact onto the tube to cause deflagration of the fulminating material up through the tube to ignite the combustible disposed in the lamp envelope.

Although the fulminating material must have a very high impact sensitivity in order to insure the reliability of lamp flashing in the finished product, it presents very substantial problems and difficulties with respect to the manufacture and handling of individual lamps in a high-speed, mass production operation. Very minor bumping or jarring of the intermediate product structure of the lamp during its manufacture can cause the fulminating material to flash. If such accidental flashing of the fulminating material occurs prior tothe introduction of the compressed oxygen atmosphere into the intermediate product structure, it goes unnoticed because the shredded combustible, even if present, does not burn. Such lamps with spent fulminating material are, of course, inoperative.

The foregoing problem is unique to flashlamps of the percussivetype. Conventional filament-ignited flashlamps may be subjected to electrical continuity checking of the filament lead wire assembly and the beads of ignition paste are visible rather than concealed within a metal tube. On the other hand, nondestructive tests, such as visual or X-ray inspection of percussive-type photoflash lamps, fail to show whether or not the fulminating material has been discharged or flashed during lamp manufacturing operation. When destructive testing techniques, such as flashing of sample lamps, show a high incidence of lamps with preflashed material, the entire production group must be scrapped because the defective lamps cannot be segregated. Such losses make the manufacture of percussive-type photoflash lamps a formidable operation, increasing the cost of the finished product to the consumer and could result in unintentional marketing of defective lamps. While the occurrence of such inadvertent ignitions might possibly be avoided or minimized by handling the lamps with extreme care on an individual basis, the cost of such a procedure would be prohibitive.

In view of the foregoing, one of the principal objects of this invention is to greatly facilitate the manufacture of percussivetype photoflash lamps on high-speed automated equipment and at the same time provide the necessary quality control attendant such manufacture. More specifically, one of the principal objects of this invention is to facilitate the segregation of prematurely flashed primer assemblies at various stages during lamp manufacturing operations as well as thereafter.

It has been found that with the use of fluorescent pigments in conjunction with an acid base indicator, a percussive flashlamp indicator spot can be effectively formulated that permits automated lamp inspection by virtue of its fluorescence and that also provides a visible change from one color to another. The technique is based on.masking of the fluorescent pigment with an acid-base indicator. An indicator is chosen such that when it is buffered on the alkaline side, the fluorescent pigment is unmasked and will fluoresce under ultraviolet light. The intensity of this fluorescence is measured 1 with a photocell. When the indicator changes to the acid side due to exposure to the combustion products of the fulminating material, a distinct color change takes place, masking the fluorescent pigment and thereby preventing it from fluorescing under ultraviolet light.

In a specific embodiment of the invention illustrated in the accompanying drawing, the single H6. is a sectional elevational view of a percussive-type photoflash lamp embodying the principles of this invention. The lamp comprises a length of glass tubing defining an hermetically sealed lamp envelope 2 constricted at one end to define an exhaust tip 4 and shaped to define a seal 6 about a primer 8 at the other end thereof. The primer 8 comprises a metal tube 10, a wire anvil l2 and a charge of fulminating material 14. A combustible such as filamentary zirconium l6 and a combustion-supporting gas such as oxygen are disposed within the lamp envelope. The wire anvil 12 is centered withinthe tube 10 and held in place by a crimp 18 just above the head 20 of the anvil. Additional means, such as lobes 22 on wire anvil 12, are also used to aid in stabilizing and supporting it substantially coaxial-within the primer tube 10 and insuring clearancebetween the fulminating' material 14 and the inside wall of the tube 10. A refractory bead 24, fused to the wire anvil 12 just above the inner mouth of the primer tube 10, eliminates burnthroughs and functions as a deflector to deflect and control the ejection of hot particles of fulminating material from the primer tube.

An indicator spotting fluid prepared in accordance with the principles of this invention comprises a pH indicator, a fluorescent pigment, a buffering agent and a binder. In a specific embodiment, it may comprise 59 percent water, 9.7 percent fluorescent pigment, 19.5 percent glycerol, 6.8 percent polyvinyl alcohol, 4.1 percent sodium bicarbonate and 0.9 percent methyl red. A small drop of this fluid is applied on the inner wall of the flashlamp envelope 2 to provide an indicator spot 26 and dried justprior to insertion of the wire anvil l2 coated with fulminating material 14 into the primer tube 10 in sea] 6. Subsequently, the combustible 16 is introduced into the lamp envelope 2, a constriction is drawn at the open end and the intermediate product is processed in the after ignition of the fulminating material. The indicator is buffered with sodium bicarbonate. Since sodium bicarbonate is basic in nature, the indicator turns yellow when mixed with such a substance. In the specific example, green fluorescent pigment was employed and it is quite compatible with methyl red. When the fluorescent pigment is mixed with the indicator, the fluorescence of the pigment is unattenuated by the yellow color of the mixture. Ignition of the fulminating material within a percussive lamp causes, masking of the fluorescent pigment by the formation of a deep red color from the indicator. Detection of the fluorescent spot by ultraviolet light is no longer possible. However, the deep red spot is clearly visible to the eye.

A binder found to be very effective is polyvinyl alcohol mixed with glycerol. Since the fluorescent pigments are water insoluble, these organic resinous materials employed are useful in suspending the fluorescent pigment in the mixture. Other resinous binders may be used provided they are compatible with the system, effecting complete suspension of the fluorescent pigment as well as good adherence. to the lamp envelope. These binders must be water soluble and permeable to the acidic vapors of the indicator. For example, other binding resins which may be employed are hydroxyethl cellulose, hydroxypropyl cellulose, methyl cellulose and polyvinylpyrollidone.

Not only may various indicators, pigments, buffering agents and binders be employed within the parameters noted above, but the relative quantities used may also be altered substantially. The amount of fluorescent pigment may vary from about 1 percent to about 40 percent, less than 1 percent being inadequate to produce a desirable level of fluorescence and more than 40 percent producing a concentration too great to be masked properly by the pH indicator. Glycerol and polyvinyl alcohol are at a ratio of about 3:1. The glycerol is present to permit functioning of the pH sensitive indicator and may range from about 5 percent to about 50 percent. The pH indicator and sodium bicarbonate are in a ratio of approximately 1:4 with the range of the sodium bicarbonate variable between about 0.1 percent to about percent. Excessive sodium bicarbonate may decrease spot sensitivity. Although we prefer to use glycerol as the humectant, other humectants such as triethylene glycol and tetraethylene glycol for example may also be employed. The selection of an indicator is governed principally by the requirement that it must mask the fluorescence of the pigment either initially or after discharge of the fulminating material. Although in the specific embodiment described above the spot fluoresces until the discharge occurs, if a different indicator, such as bromocresol purple for example were employed, the spot would not begin to fluoresce until after burning of the fulminating material had occurred.

One of the principal advantages of the spotting technique of our invention is that it makes possible the use of two separate and distinct detection methods. Due to the color change of the spot, visual inspection can be employed to detect premature ignition of the fulminating material. In addition, the distinct masking of the pigment permits no fluorescence to occur and thus no response by the photocell detector. This procedure is fail-safe in that any lamps not spotted would be rejected instead of passed as good lamps and it readily lends itself to adaption to automated production. It would make possible 100 percent inspection of all lamps throughout the production process, automatically rejecting those which have flashed inadvertently. The rate of change of the spot from one condition to another is rapid enough to make it acceptable for use in high-speed automated production.

In general, fluorescent dyes and pigments are easily adapted for use as indicator spots in percussive lamps. Through their use, several other methods of detection for ignition of fulminating material may be employed. An indicator spot may initially be masked from fluorescing and then, after ignition of the fulminating material, be allowed to fluoresce. Fluorescent dyes which are water soluble and pH sensitive may also be employed and used for both visual and automatic detection.

What we claim is: 1

1. A photoflash lamp comprising:

an hermetically sealed, light-transmitting envelope;

a quantity of filamentary combustible material located within said envelope;

a combustion-supporting gas in said envelope;

a primer secured to and extending from one end of said envelope, said primer including a charge of fulminating material;

and means located within said envelope for indicating the functional condition of said fulminating material, said means comprising a pH indicator responsive to the combustion products of said fulminating material and a fluorescent pigment insensitive thereto.

2. The combination of claim 1 in which said pH indicator masks said fluorescent pigment when exposed to the combustion products of said fulminating material, thereby preventing it from fluorescing under ultraviolet light but permittin g it to be still visible to the eye.

3. The combination of claim 1 in which said pH indicator normally masks said fluorescent gigment but which, when exposed to the combustion produc of said fulminating material, exposes said fluorescent pigment thereby permitting it to fluoresce under ultraviolet light.

4. The combination of claim 1 in which said pH indicator is acid based and buffered on the alkaline side whereby exposure thereof to the combustion products of the fulminating material causes said indicator to change to the acid side, thus masking said fluorescent pigment and thereby preventing it from fluorescing under ultraviolet light but permitting it still to be visible to the eye.

5. The combination of claim 1 in which said indicating means is a spot of a fluid formulated from the combination of a pH indicator, a fluorescent pigment, a buffering agent and a binder.

6. The combination of claim 5 in which the binder is a water soluble organic resinous material permeable to the acidic vapors of ignited fulminating material. 

1. A photoflash lamp comprising: an hermetically sealed, light-transmitting envelope; a quantity of filamentary combustible material located within said envelope; a combustion-supporting gas in said envelope; a primer secured to and extending from one end of said envelope, said primer including a charge of fulminating material; and means located within said envelope for indicating the functional condition of said fulminating material, said means comprising a pH indicator responsive to the combustion products of said fulminating material and a fluorescent pigment insensitive thereto.
 2. The combination of claim 1 in which said pH indicator masks said fluorescent pigment when exposed to the combustion products of said fulminating material, thereby preventing it from fluorescing under ultraviolet light but permitting it to be still visible to the eye.
 3. The combination of claim 1 in which said pH indicator normally masks said fluorescent pigment but which, when exposed to the combustion products of said fulminating material, exposes said fluorescent pigment thereby permitting it to fluoresce under ultraviolet light.
 4. The combination of claim 1 in which said pH indicator is acid based and buffered on the alkaline side whereby exposure thereof to the combustion products of the fulminating material causes said indicator to change to the acid side, thus masking said fluorescent pigment and thereby preventing it from fluorescing under ultraviolet light but permitting it still to be visible to the eye.
 5. The combination of claim 1 in which said indicating means is a spot of a fluid formulated from the combination of a pH indicator, a fluorescent pigment, a buffering agent and a binder.
 6. The combination of claim 5 in which the binder is a water soluble organic resinous material permeable to the acidic vapors of ignited fulminating material. 